Fluid meter with improved piston guidance

ABSTRACT

The invention relates to a fluid meter ( 27 ) comprising a housing ( 28 ) defining at least one crankcase ( 29 ) and two cylinders ( 25, 26 ), a crankshaft ( 11 ) disposed in the crankcase ( 29 ), two pistons ( 3, 4 ) respectively mounted in the cylinders ( 25, 26 ) for reciprocal movement, a first connecting rod ( 12 ) connected to one of the pistons ( 3 ) and to the crankshaft ( 11 ) for rotating the crankshaft ( 11 ) in response to the movement of the one piston ( 3 ), and a second connecting rod ( 13 ) connected to the other piston ( 4 ) and to the crankshaft ( 11 ) for rotating the crankshaft ( 11 ) in response to the movement of the other piston ( 4 ), wherein the first and second connecting rods ( 12, 13 ) have yoke slots ( 16, 17 ) for receiving a crank pin ( 19 ) radially offset from the crankshaft ( 11 ). The invention is characterised in that the first connecting rod ( 12 ) has a guiding rod ( 20 ) extending in a longitudinal direction of the cylinders, the guiding rod ( 20 ) being adapted to engage a corresponding cavity ( 22 ) in the second connecting rod ( 13 ) to support and guide the connecting rods ( 12, 13 ) in relation to each other during movement. The invention further relates to a multiple fluid meter assembly ( 61 ) comprising at least two fluid meters ( 27 ) as defined above, and to a fuel dispensing unit comprising a fluid meter ( 27 ) or a multiple fluid meter ( 61 ) as defined above.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application pursuant to 35 U.S.C.§371 of PCT Application No. PCT/EP2010/070810, filed Dec. 28, 2010, andentitled “Fluid Meter With Improved Piston Guidance,”the entire contentsof which is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a fluid meter for volumemeasurement of a flowing fluid. More particularly, the present inventionrelates to a fluid meter as defined in the introductory part of claim 1,a multiple fluid meter assembly as defined in claim 11, and a fueldispensing unit as defined in claim 14.

BACKGROUND ART

Fluid meters are widely used for most kinds of fluids in differentapplication areas. Fluid meters are for example used in fuel dispensingpumps for retail sale of motor fuel, providing a means for measuring thequantity dispensed from the pump. The measured volume is typicallycommunicated to a register, displaying the dispensed volume and theprice.

A fluid meter commonly used for fuel dispensers is shown by Ainsworth,U.S. Pat. No. 2,756,726. In this disclosure a meter having a multiplepiston hydraulic motor is used. Fluid is allowed to enter cylinders andcause reciprocation of the pistons. The pistons are connected to ashaft, that will rotate as an effect of the reciprocation. A rotaryvalve, coupled to the shaft, admits liquid to the cylinders or permitsflow to the outlet connections, in proper timed relation. The fluidmeter utilizes what may be termed “hypothetical” cylinders, mechanicallyand hydraulically cooperating with the cylinders and pistons which arestructurally existent.

This is accomplished by arranging the ports and the rotary valve so asto sequentially admit fluid to both the crankcase and the ends of thecylinders at the same time as fluid is withdrawn from the cylinders. Thefluid volume admitted to, or withdrawn from, the crankcase is thealgebraic sum of the volume withdrawn from, or admitted to, thecylinders. Two pistons, actuated through the valve mechanism,advantageously 120 degrees out of phase, thus perform the workequivalent of three pistons. This reduces the actual number of cylindersrequired for a given capacity, reduces internal friction and pulsation,and achieve smoother operation. The two pistons are attached viaconnecting rods to a crankshaft with a radially offset crank pin. Thecrank pin engages a yoke in each connecting rod so that thereciprocating movement of the two pistons is transformed into a rotarymotion of the crankcase in accordance with the Scotch Yoke typeprinciple. To accomplish the phase differences between the pistons, thetwo physical cylinders are oriented with an angle of 120 degrees betweentheir respective centre axis.

The Ainsworth fluid meter has several drawbacks, as e.g. the requirementof special piston guide barrels, the arrangement of cylinders and guidebarrels is difficult to mould or cast and machine, and the register isdriven by a shaft extending through the meter housing with accompanyingrisk of leakage.

A similar fluid meter is disclosed by Spalding, U.S. Pat. No. 5,686,663and WO 98/49530. This fluid meter aims at eliminating the drawbacks ofthe Ainsworth fluid meter. Thus, the two angled cylinders of Ainsworthare aligned along a common centre axis to eliminate the bulkyconstruction of Ainsworth. To accomplish the same piston reciprocity,the crankshaft is modified with an extra crank arm. The in-lineconstruction is advantageous when several meters have to be mounted inone dispenser, which is the normal case in most modern fuel dispensers.

The Spalding fluid meter, however, is not without some drawbacks. Theconnecting rods that are connected to the pistons and are driven by thecrankshaft via two crank arms, have to be guided in some way to keep astraight movement and no wear on the cylinder walls, Spalding has twosolutions to that problem. According to the first solution the pistonshave guiding rods extending in a direction away from the crank shaft andtowards the end of the cylinder. The cylinder end piece has a receivingcavity for the guiding rod to keep the piston and the connecting rod toreciprocate along a straight line. The other solution suggest that aguiding tap is extending from one connecting rod, engaging the otherconnecting rod to guide the connecting rods in one another.

Both of the solutions for guiding the connecting rods according toSpalding have drawbacks. The first solution has the drawback of usingspace requiring cavities in the cylinder ends, causing the cylinderlength to be increased. The second solution has the drawback of beingsubject to wear. When the connecting rods are worn measurement accuracywill be affected, which is not acceptable in a dispenser dispensingsomething as valuable as fuel.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the current state ofthe art, to solve the above problems, and to provide an improved fluidmeter that is easier to manufacture, more robust, more reliable, andmore precise than previous fluid meters. This is solved by usingconnecting rods that are guided in each other in a way that minimizeswear to the guiding arrangement of the rods, while keeping the size ofthe connecting rods and guiding arrangement to a minimum.

According to one aspect, the present invention provides a fluid metercomprising a housing defining at least one crankcase and at least twocylinders, a crankshaft disposed in the crankcase, at least two pistonsrespectively mounted in the cylinders for reciprocal movement, a firstconnecting rod connected to one of the pistons and to the crankshaft forrotating the crankshaft in response to the movement of the one piston,and a second connecting rod connected to the other piston and to thecrankshaft for rotating the crankshaft in response to the movement ofthe other piston, wherein the first and second connecting rods have yokeslots for receiving a crank pin radially offset from the crankshaft. Thefluid meter is characterised in that said first connecting rod has aguiding rod extending in a longitudinal direction of said cylinders,said guiding rod being adapted to engage a corresponding cavity in saidsecond connecting rod to support and guide the connecting rods inrelation to each other during movement.

The concept of having a guiding rod that guide the two connecting rodsand pistons in the fluid meter cylinders through a solution where theguiding rod is received in a cavity of the other connecting rod has theadvantage over the prior state of the art in that it creates a sturdyguiding connection, reducing wobbling or fluctuations sideways in thecylinders. The guiding solution will also suffer much less from wearthan previous solutions since fluctuation sideways in the cylinders isreduced. Having the guiding rod along the side of the connecting rod,the cavity of the other rod naturally being placed correspondingly, theguiding arrangement will not affect the length of the connecting rods.The connecting rods can thus be minimized in length which is importantto reduce the fluid meter size.

The second connecting rod may have a guiding rod extending in alongitudinal direction of said cylinders, said guiding rod being adaptedto engage a corresponding cavity in said first connecting rod. Thisfeature will make it possible to manufacture the two connecting rods asidentical pieces, reducing manufacturing costs. It will also create aneven more sturdy construction, having the same benefits as discussedabove, i.e. reduced sideways movement and reduced wears of the guidingarrangement of the connecting rods.

The cavity of each connecting rod may extend along more than half thelength of said connecting rod in its longitudinal direction. Naturallythe guiding rod of each one of the connecting rods has a correspondingfree length that is equal to the depth of the cavity. The free length isthe part of the guiding rod that is not covered by the material of theconnecting rod. Since the cavity length and the corresponding guidingrod is long, a relatively large overlap between the guiding rod and thecavity will occur. The overlap is 20-80%, preferably 30-70% and morepreferably 40-60% of the length of the connecting rod. The relativelylarge overlap will enhance the sturdiness of the construction of the rodguiding arrangement and reduce sideways movement and reduce wear. Theoverlap will of course vary depending on the position of the pistons.But due to the long guiding rod compared to the length of the connectingrod, the overlap will be large also when the connecting rods are as farapart as possible.

The connecting rod may be made of a hard plastic and the guiding rod maybe made of metal. The guiding rod may then be moulded into the guidingrod. The connecting rods could however also be made of metal, eithermoulded or made of a metal sheet, as in the prior art. Making theconnecting rods of plastic has the advantage of cheap manufacturingcosts and low weight. Low weight will increase the efficiency of thefluid meter since the resistance force that has to be overcome by thefluid to move the pistons will be reduced.

The connecting rods may be connected to the crankshaft by one commoncrank pin that is radially offset from the crankshaft; an axis throughthe endpoints of the yoke slot of one connecting rod may form an anglealpha with the alignment axis of the two cylinders; and an axis throughthe endpoints of the yoke slot of the other connecting rod may formanother, different angle beta with said alignment axis, so that thecorresponding pistons reciprocate out of phase.

It should, however be noted that the inventive guiding arrangement isequally useful for the traditional yoke arrangement according to theScotch Yoke principle, where the yokes are oblong having theirlongitudinal direction perpendicular to the piston movement. As pointedout in the background art section, this will require that either thecylinders are angled 120 degrees to one another or the use of two crankarms.

Using yoke slots that extend along a straight line between the endpointsof the yoke slot is the easiest way to generate piston movement with amotion speed following a harmonic sinus shape. It should however benoted that other shapes of the yoke slots could be used, e.g. where theyoke is bent along a suitable curve. The design of the inlet/outletvalve of the fluid meter casing could e.g. require a specialreciprocating piston movement, invoked by the yoke slots, to match itsdesign.

The settings of the yoke slots are arranged so as to cause the pistonsto reciprocate out of phase even though the cylinders are aligned alongthe same centre axis. Using normal transversal yoke slots, such as inthe Spalding patent described above, two crank arms are necessary toachieve piston movements that are out of phase in such a geometry. Usingthe yoke slots according to the invention only one crank arm isnecessary. There are several benefits of using only one crank arm forthe movement of the pistons. The number of components are reduced,leading to reduced material costs. The manufacturing procedure issimplified leading to cheaper production costs. One single crank arminstead of two leads to a crankshaft assembly that is a more robust andrigid unit. Further, the problem of providing the correct angle betweentwo crank arms is eliminated as there is only one crank arm.

Each one of the yoke slots of said two connecting rods may be adapted toextend along a straight line between said endpoints. As mentioned above,this is the easiest way to generate piston movement with a motion speedfollowing a harmonic sinus shape and is therefore preferred at present.

The angles alpha and beta may be chosen so that the pistons reciprocateapproximately 60° out of phase.

It is advantageous that the yokes, and thus also the connected pistons,reciprocate approximately 60° out of phase to achieve a smooth operationof the fluid meter. To be able to construct the housing in a simple andfairly symmetric manner, a phasing of the pistons 60° out of phasetogether with a proper inlet/outlet valve design and a geometry wherethe cylinders are directed from each other, i.e. 180° angled from oneanother, will allow the fluid flow to enter and exit the two cylindersand the “hypothetical” cylinder in the crankcase, i.e. in between thereciprocating pistons, one by one in a smooth motion with a phase offsetby 120° between the operation of the cylinders.

The angle alpha of the yoke slots of the fluid meter may be less than90° and the angle beta may be more than 90°. More preferably alpha maybe approximately 60° and beta may be approximately 120°. The latterangle setting will cause the pistons to reciprocate 60° out of phase andthe operation of the cylinders will thus be 120° out of phase aspreferred due to the 180° angle between the two physically existingcylinders.

Another advantage of using oblique settings of the yoke slots, e.g. withangles as described above, is that manufacturing of the fluid meter issimplified. Not only will the crank shaft be simpler, having only onecrank arm and one crank pin, but the setting of the angles creating theout-of-phase piston movements will be made in the manufacturing processof the yoke slots instead of in the mounting of two crank arms on thecrank shaft as in the prior art of Spalding. Accurate and preciseformation of the yoke slots is fairly simple to achieve. The yokes andslots can be manufactured by moulding, punching a metal sheet, cuttingetc. All of these methods are simple and they do not differ from the wayother yokes are manufactured. This means that the manufacturing changesin the production of the yokes that are invoked by the present inventionwill be very small.

According to the present invention it is further preferred to provide afluid meter of the above type where ports are defined in the housing incommunication with the cylinders and the crankcase, and furthercomprising a port valve mounted on the crankshaft for rotation therewithand having a plurality of ports for sequentially registering with theports in the housing for distributing fluid into and from the cylindersand the crankcase to control the movement of the pistons. The port valveas described above will ensure precise volume flow through the cylindersof the fluid meter.

The fluid meter may comprise at least one wheel coupled to thecrankshaft and may have at least one magnetic pole, and at least onesensor to detect the influence of the at least one magnetic pole and togenerate a signal corresponding to the flow of the fluid into and fromthe corresponding cylinders and the crankcase.

According to another aspect the present invention provides a multiplefluid meter assembly comprising at least two fluid meters of the abovetype. Such an assembly will provide a compact design when multiple fluidmeters are required.

The at least two fluid meters may be arranged such that their alignmentaxes are parallel. An assembly with parallel fluid meters will provide ameter assembly that is very compact. This is often an important criteriain modern fluid dispensers, where many fluid meters are required and thefluid dispenser unit design require the internal equipment to be small.

The fluid inlet and the fluid outlet of one fluid meter may communicatewith the fluid inlet and the fluid outlet of another fluid meter,respectively, so as to connect the individual fluid meters in parallel.

According to yet another aspect the present invention provides a fueldispensing unit for refueling vehicles, comprising a fluid meter or amultiple fluid meter assembly of the types described above. The fluidmeter or fluid meter assembly according to the present invention isespecially suitable for fuel dispensers due to its reliability andaccurate measurement capabilities.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, as well as additional objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following illustrative and non-limiting detaileddescription of preferred embodiments of the present invention, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 a is an exploded diagram of connecting rods having slotted yokesand a crank shaft having two crank arms of a fluid meter according toprior art.

FIG. 1 b is a perspective view of a mounted assembly of the prior art ofFIG. 1 a.

FIG. 2 a is an exploded diagram of connecting rods, a crankshaft havingone crank arm, a rotating valve, a magnetic wheel and a transduceraccording a preferred embodiment of a fluid meter according to thepresent invention.

FIG. 2 b is a perspective view of a mounted assembly of FIG. 2 a.

FIG. 3 is a cross sectional view of the fluid meter according to theinvention taken along the axis of the aligned cylinders, correspondingto the line III of FIG. 2 b.

FIG. 4 is a cross sectional view along the line IV in FIG. 3 of thefluid meter according to the invention.

FIG. 5 a is a top view of the rotary valve of the fluid meter.

FIG. 5 b is a cross sectional view of the rotary valve of the fluidmeter according to the invention.

FIG. 6 is a plan view showing the ports of a rotary valve superimposedover a valve seat of the fluid meter in FIG. 3.

FIG. 7 is an isometric view of a unitary assembly incorporating twofluid meters similar to the meter of FIGS. 1-6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1 a and 1 b shows a pair of connecting rods, 1, 2, according toprior art (U.S. Pat. No. 5,686,663 to Spalding et al), each connected toa piston, 3, 4, as described in the prior art. The connecting rods, 1,2, have Scotch yoke portions, 5, 6, with oblong yoke slots, 7, 6. Thecentre axes of the yoke slots are perpendicular to the centre axes ofthe connecting rods, 1, 2. To move the connecting rods, 1, 2, and thusalso the pistons, 3, 4, with a phase difference of 60°, as described inthe prior art of Spalding, the yoke portions, 5, 6, will have to bedriven by different crank arms, 9, 10, of the crankshaft, 11 as depictedin FIGS. 1 a and 1 b.

FIGS. 2 a and 2 b shows the connecting rods 12, 13 of a preferredembodiment of the present invention, the connecting rods 12, 13, havingyoke slots 16, 17. The connecting rods 12, 13 are connected by theguiding arrangement according to the present invention. The guiding rod20 of each connecting rod 12, 13 are engaging the cavity 22 of the otherconnecting rod. In the embodiment of FIGS. 2 a and 2 b, the guiding rods20 are moulded into in the fastening sections 14 of the plasticconnecting rods. The cavities 22 naturally has the same length as thefree end, i.e. the end that is outside the moulded fastening section 14.

To perform a reciprocating movement of the pistons, 3, 4, using only onecrank arm, 18, the centre axes of the oblong yokes slots, 16, 17, areeach angled 30° compared to the perpendicular direction to the centreaxes of the connecting rods 1, 2. The combined angle between the centreaxes of the oblong yoke slots of the two connecting rods, 12, 13, isthus 60°. This arrangement of the yoke slots will invoke the samemovement of the connecting rods, 12, 13, and thus also the pistons, 3,4, as the prior art, i.e. a reciprocating movement of the pistons 60°out of phase, but with the use of only one crank arm, 18, and one crankpin, 19.

In FIG. 3 the reference numeral 27 designates a flow meter according tothe present invention. The flow meter 27 includes a flow meter body 28having a crankcase portion 29 (indicated by the broken lines) andopposing, axially aligned, first and second cylinder portions, 25 and26, respectively, extending outwardly from the crankcase (from thebroken lines). The head ends of the cylinder portions 25 and 26 arecapped by first and second head end cover plates 30 and 31,respectively.

A magnetic wheel 32 is connected to the crankshaft 11 at the centre ofthe magnetic wheel 32. A series of magnetic poles (not shown) areincorporated in the magnetic wheel 32 angularly spaced about the outercircumference of the wheel 32.

A Hall effect transducer 33 having two sensors, well known in the art,is mounted within close proximity to the magnetic wheel 32. Due to theproximity of the sensors to the wheel 32, the sensors can detectfluctuations in the magnetic influence of the magnetic poles of thewheel 32 when the wheel 32 rotates. In response to such detection, thetransducer 33 generates a pulsed signal proportional to the rate ofrotation of the wheel 32. The two sensors are, furthermore, horizontallyspaced so that the direction of rotation of the magnetic wheel 32 can bedetermined by identifying which of the two sensors first detects themagnetic influence of a particular pole.

A ball bearing assembly 34 is fitted in a small bore 35 in the meterbody 28. A crankshaft 11 is rotatably disposed in the bearing assembly34. The crankshaft 11 has a vertical orientation bearing laterallyagainst the bearing assembly 34. The upper portion of the crank shaft 11extends above the bearing assembly 34 and is shaped to receive a rotaryvalve more thoroughly discussed with reference to FIGS. 5 and 6 below. Acrank arm 18 is connected to the lower portion of the crankshaft 11 andextends radially outwardly from the crankshaft. A crankpin 19 extendsdownwardly from the radially outer part of the crank arm 18 through afirst roller bearing 36 and a second roller bearing 37, the secondroller bearing 37 being located below the first roller bearing 36.

Referring to FIG. 3, the flow meter 27 further includes first and secondpistons 3, 4, disposed in the cylinders 25 and 26, respectively. Firstand second connecting rods, 12, 13, drivingly connect the respectivepistons 19, 20, to the respective first and second roller bearings, 36,37. The connecting rods 12, 13 are hence connected to the crankshaft viathe roller bearings, 36, 37. The connecting rods 12, 13 are more clearlyshown in FIGS. 2 a and 2 b. The first and second connecting rods, 12, 13are in this particular embodiment moulded in plastic material havingfirst and second oblong slotted yokes, 16, 17 for slidingly engaging therespective first and second roller bearings, 36, 37. The oblong slottedyokes, 16, 17 do in this embodiment have straight central axes with anangle of 60° between the respective centre axis. The first and secondslotted yokes 16, 17, have centre axes with angles of 120° and 60°,respectively, to the centre axis of the axially aligned first and secondcylinder portions 25 and 26.

The guiding arrangement comprising the guiding rods 20, rigidly fastenedin the connection rods at the fastening portion 14, and the cavities 22corresponding to the guiding rods 20, present a rigid guidingarrangement. As the piston 3 is moved to the left by fluid entering thecylinder volume 40 in the fluid meter, the connecting rod 12 is moved tothe left pressing its guiding rod 20 further into the cavity 22 of theother connecting rod 13. The guiding rod 20 of the other connecting rod13 is naturally correspondingly pressed further into the cavity 22 ofthe connecting rod 12. Since the guiding rod has a length correspondingto a large portion of the entire length of the connecting rod, thelength of the contact are between each of the guiding rods 20 and thecorresponding cavities 22 will be large, leading to a stable guidanceand low wear.

Referring to FIG. 3, the pistons 3, 4, have circular recesses, 38, 39,for receiving gaskets (not shown). The gaskets are made of a resilientmaterial to seal the cylinder head chambers 40 and 41 from the crankcasechamber 42 defined by the crankcase portion 29 and the parts of thecylinder portions 25, 26 that are on the inner sides (facing thecrankcase) of the pistons 3 and 4. The two pistons 3, 4, thus dividesthe cylinder volumes combined with the crank case portion volume inthree chambers, sealed from each other, the head chambers 40, 41 and thecrankcase chamber 42.

FIG. 6 shows the valve seat 43 as seen from the top of the flow meter 27of FIG. 3. The valve seat 43 includes first, second and third arcuateports, 44, 45, 46, which each cover an arc about the crankshaft bore 47of approximately 80° and are angularly spaced apart approximately 40°between ports. Referring to both FIGS. 3 and 6 the first port 44 is influid communication with the first head end chamber 40 via a firstpassageway 48 formed in the fluid meter body 28. The second port 45 isin fluid communication with the second head end chamber 41 via a secondpassageway 49 formed in the fluid meter body 28. Referring to FIGS. 6and 4, the third port 46 is in fluid communication with the crankcasechamber 42 via a third passageway 50 formed in the fluid meter body 28.

Referring to FIG. 5 a, a rotary valve 51 is positioned on top of thevalve seat 43 to control the admission and discharge of a fluid into andout of the first, second, and third ports 44, 45, 46. The rotary valve51, with reference to FIGS. 5 a and 5 b, includes a hole 52 formed inthe center thereof through which the crankshaft 11 extends for rotatablycoupling the valve 51 to the crankshaft 11. Referring to FIGS. 5 and 6,the rotary valve 51 further includes an arcuate inlet port 53 and anarcuate outlet port 54 axially and radially aligned to alternatelyregister with the first, second, and third arcuate ports 44, 45, 46 ofthe valve seat 43 when the valve 51 is rotated by the crankshaft 11 Theports 53, 54 each cover an arc about the hole 52 of approximately 100°and are angularly spaced apart approximately 80° between ports.

As further shown in FIGS. 3 and 4, a mounting flange (or meter dome) 55is secured to the top of the flow meter body 28. A supply chamber 56 isformed in the flange for supplying fluid to the inlet port 53 of therotary valve 51. A supply port 57 formed in the flange provides fluidcommunication between the supply chamber 56 and fluid supply lines (notshown). Similarly, an annular discharge chamber 58 is formed in theflange 55 for receiving fluid discharged from the outlet port 54 of therotary valve 51. A discharge port 59 provides fluid communicationbetween the discharge chamber 58 and fluid discharge lines (not shown).

FIG. 6 further depicts one instantaneous position of the rotary valveports 53, 54 (shown in phantom) superimposed over the first, second, andthird ports 44, 45, 46 of the valve seat 43. In operation, the rotaryvalve 51 is rotated by the crankshaft 11 in a counterclockwise directionas indicated by the arrow 60. Accordingly, the inlet and outlet ports53, 54 sequentially register with each of the ports 44, 45, 46. As shownin FIG. 6, the inlet port 53 is registered with the third port 46 andthe outlet port 54 is registered with the second port 45. Registrationof the inlet port 53 with the first port 44 is depicted as impending.Because each of the ports 44, 45, 46 cover an angle of approximately 80°and each of the rotary valve ports 53, 54 cover an angle ofapproximately 100°, each port 44, 45, 46 alternately registers with theinlet port 53 for 180° of rotation of the crankshaft 1 and then with theoutlet port 54 for 180° of rotation. It can be appreciated that theinlet port 53 or the outlet port 54 may register with one or two, butnot all three, of the ports 44, 45, 46 simultaneously. The ports 44, 45,46 may, however, register with only one of the ports 53, 54 at a time.

To more fully illustrate the operation of the flow meter 27, and withreference to FIG. 3, it will be assumed that, initially, the flow meterbody 28 is filled with fluid, the crankshaft 11 is rotated to place thefirst piston 3 in as close proximity to the head cover 30 as possible(i.e., a “top dead centre” position), the second piston 4 leads thefirst piston 3 by a phase angle of 60°, and the rotary valve ports 53,54 are related to the first, second, and third ports 44, 45, 46 as shownin FIG. 6 a fluid, such as gasoline from an external source (not shown),is then supplied through the supply port 57 and passed through thesupply chamber 56, the inlet port 53 of the rotary valve 51, and, inaccordance with FIG. 6, through the third port 46. The fluid then flowsthrough the third passageway 50 (FIG. 4) and into the crankcase chamber42 where it applies pressure to displace the second piston 4 outwardly(away from the crankshaft 11). The first piston 3 resists outwardmovement since it is in a top dead centre position. The outward movementof the second piston 4 expels fluid from the second chamber 41 therebycausing the fluid to pass through the second passageway 49, the outletport 54 of the rotary valve 51, the discharge chamber 58, and outthrough the discharge port to 59 to a discharge line (not shown). Themovement of the second piston 4 also drives the crankshaft 11 via thesecond connecting rod 13. Accordingly, the crankshaft 11 imparts counterclockwise rotation to the rotary valve 51 and the inlet port 53 beginsto register with the first port 44. Fluid in the supply chamber 48 thenbegins to flow through the inlet port 53 of the rotary valve 51 andthrough the first port 44. The fluid then flows through the firstpassageway 48 into the first chamber 40 and applies pressure to displacethe first piston 3 inwardly (towards the crankshaft 11), therebyeffecting further rotation of the crankshaft 11 and the rotary valve 51.The process continues according the principles described herein. As aresult, the pistons 3, 4 reciprocate in the cylinders 25, 26,respectively, thereby rotating the crankshaft 11, the attached rotaryvalve 51, and the magnetic wheel 32. The sensors in the Hall effecttransducer 33 detect the consequent fluctuation in the magneticinfluence of the magnetic poles on the wheel 32 and generate a pulsedsignal which is proportional to the flow rate of the fluid passingthrough the flow meter 27. Although not clear from the drawings, it isunderstood that the pulsed signal may be employed to drive an electroniccounter and indicator for recording the volume and total value of fluid,such as gasoline, dispensed through the flow meter 27.

The inlet and outlet ports 53, 54 of the rotary valve 51 and the ports44, 45, 46 cooperate such that the volume of fluid admitted to, orwithdrawn from, the crankcase chamber 42 is equal to the algebraic sumof the volume respectively withdrawn from, or admitted to, the head endchambers 40, 41. Thus the crankcase chamber 42 provides what may betermed a “blind” or “hypothetical” piston and cylinder, mechanically andhydraulically cooperating with the pistons 3, 4 which are structurallyexistent. Thus the meter operates hydraulically and mechanically like athree piston meter or hydraulic motor although it only has the physicalcomponents of a two piston meter or motor. It should be noted that theflow into and out of the flow meter 27 is substantially constant. Thisconstant flow results from reciprocating the axially-aligned pistons 3,4 60° out of phase and from utilizing yokes 16, 17 as described above,which are substantially harmonic in conformity with Scotch Yokes.

Thus, as a result of all of the foregoing, the fluid meter of thepresent invention is compact, yet cost-efficient and mechanicallyefficient.

It is understood that the yoke slots of the invention, could have othershapes. The yokes could e.g. be curved to accomplish a perfect sinefunction movement or any modification of a periodic sine function.

It is further understood that multiple flow meters 27 may be integratedinto a single assembly to gain several advantages over the single flowmeter described hereinabove. For example, a duplex flow meter assembly61 wherein two fluid meters 27, as depicted in FIG. 7, are integratedtogether, would facilitate the construction of gasoline dispenser pumpstations having two, four, six, or eight gasoline dispensers.Furthermore, a duplex flow meter 61 would only require a single meterbody, meter dome, and end cover, thereby economizing on manufacturingcosts. Installation of duplex flow meters 61 is facilitated as a resultof simplified mounting and pipe work and the reduced cabinet sizerequired to house a duplex fluid meter. Flexibility is also enhancedbecause a duplex flow meter could also serve a single hose outlet attwice the speed of delivery of a single unit flow meter.

It is further understood that the ports 44, 45, 46, 53, 54 may coverarcs of a number of different angles and, moreover, may have non-arcuateshapes.

It is still further understood that the supply port and the dischargeport may instead be utilized as discharge and supply ports respectively.Furthermore, the supply and discharge lines connected thereto may bearranged for measuring the volume of any fluid that flows through anyline. For example, in addition to measuring a fluid, such as gasoline,that flows from a dispenser, the meter could be used to measure thevolume of water flowing from a pipe into a structure such as aresidential house or other building.

It is understood that other variations in the present invention arecontemplated and in some instances, some features of the invention canbe employed without a corresponding use of other features. Accordingly,it is appropriate that the appended claims be construed broadly in amanner consistent with the scope of the invention.

The invention claimed is:
 1. A fluid meter comprising: a housingdefining at least one crankcase and at least two cylinders; a crankshaftdisposed in the crankcase; at least two pistons respectively mounted inthe cylinders for reciprocal movement; a first connecting rod connectedto one of the pistons and to the crankshaft for rotating the crankshaftin response to the movement of the one piston; and a second connectingrod connected to the other piston and to the crankshaft for rotating thecrankshaft in response to the movement of the other piston, wherein thefirst and second connecting rods have yoke slots for receiving a crankpin radially offset from the crankshaft, and wherein said firstconnecting rod has a guiding rod extending in a longitudinal directionof said cylinders, and said guiding rod engages a corresponding cavityin said second connecting rod to support and guide the connecting rodsin relation to each other during movement.
 2. A fluid meter according toclaim 1, wherein said second connecting rod has a guiding rod extendingin a longitudinal direction of said cylinders, and said guiding rodengages a corresponding cavity in said first connecting rod.
 3. A fluidmeter according to claim 1, wherein said cavity extends along more thanhalf the length of said connecting rod in its longitudinal direction. 4.A fluid meter according to claim 1, wherein the connecting rods areconnected to the crankshaft by one common crank pin, wherein an axisthrough the endpoints of the yoke slot of one connecting rod forms anangle alpha with the alignment axis of the two cylinders, and wherein anaxis through the endpoints of the yoke slot of the other connecting rodforms another, different angle beta with said alignment axis, so thatthe corresponding pistons reciprocate out of phase.
 5. A fluid meteraccording to claim 4, wherein each one of the yoke slots of said twoconnecting rods extends along a straight line between said endpoints. 6.A fluid meter according to claim 4, wherein said angles alpha and betaare chosen so that the pistons reciprocate approximately 60° out ofphase.
 7. A fluid meter according to claim 4, wherein alpha is less than90° and beta is more than 90°.
 8. A fluid meter according to claim 4,wherein alpha is approximately 60° and beta is approximately 120°.
 9. Afluid meter according to claim 1, wherein ports are defined in thehousing in communication with the cylinders and the crankcase, andfurther comprising a port valve mounted on the crankshaft for rotationtherewith and having a plurality of ports for sequentially registeringwith the ports in the housing for distributing fluid into and from thecylinders and the crankcase to control the movement of the pistons. 10.A fluid meter according to claim 1, further comprising at least onewheel coupled to the crankshaft and having at least one magnetic pole,and at least one sensor to detect the influence of the at least onemagnetic pole and to generate a signal corresponding to the flow of thefluid into and from the corresponding cylinders and the crankcase.
 11. Amultiple fluid meter assembly, comprising: at least two fluid meterscomprising a housing defining at least one crankcase and at least twocylinders, a crankshaft disposed in the crankcase, at least two pistonsrespectively mounted in the cylinders for reciprocal movement, a firstconnecting rod connected to one of the pistons and to the crankshaft forrotating the crankshaft in response to the movement of the one piston,and a second connecting rod connected to the other piston and to thecrankshaft for rotating the crankshaft in response to the movement ofthe other piston, wherein the first and second connecting rods have yokeslots for receiving a crank pin radially offset from the crankshaft, andwherein said first connecting rod has a guiding rod extending in alongitudinal direction of said cylinders, and said guiding rod engages acorresponding cavity in said second connecting rod to support and guidethe connecting rods in relation to each other during movement.
 12. Amultiple fluid meter assembly according to claim 11, wherein the atleast two fluid meters are arranged such that their alignment axes areparallel.
 13. A multiple fluid meter assembly according to claim 11,wherein the fluid inlet and the fluid outlet of one fluid metercommunicate with the fluid inlet and the fluid outlet of another fluidmeter, respectively, so as to connect the individual fluid meters inparallel.
 14. A fuel dispensing unit for refueling vehicles, comprising:a fluid meter comprising a housing defining at least one crankcase andat least two cylinders, a crankshaft disposed in the crankcase, at leasttwo pistons respectively mounted in the cylinders for reciprocalmovement, a first connecting rod connected to one of the pistons and tothe crankshaft for rotating the crankshaft in response to the movementof the one piston, and a second connecting rod connected to the otherpiston and to the crankshaft for rotating the crankshaft in response tothe movement of the other piston, wherein the first and secondconnecting rods have yoke slots for receiving a crank pin radiallyoffset from the crankshaft, and wherein said first connecting rod has aguiding rod extending in a longitudinal direction of said cylinders, andsaid guiding rod engages a corresponding cavity in said secondconnecting rod to support and guide the connecting rods in relation toeach other during movement.